Rear-vision optical instrument



H. M MASTER ET AL 2,374,027

REAR VISION OPTICAL INSTRUMENT 4 Sheets-Sheet 1 Filed Dec. 26, 1941 FKHNK f7. ROOM/3N.

(Ittorneg Ap 1945. H. A. MCMASTER ETAL' 2,374,027

NEAR VISION OPTICAL INSTRUMENT Filed Dec. 26, 1941 4 Sheets-Sheet 2 Jrmentord HflKOLO A. M MHSTEK FKHNK A. room/v.

April 1 H. A. MCMASTER ET AL 2,374,027

REAR VISION OPTICAL INSTRUMENT Filed necqzs, 1941 4-Sheets-Sheet 3 attorney April 1945. H. A. McMAsTER ETAL 4,027

BEAR VISION OPTICAL INSTRUMENT 4 Shets-Sheet 4 {HI-ed Dec. 26,. 1941 Snvntors H/JKOLD f). f'F/"HJTEK.

FKANK Axon/1m. 4 ,4 1

"mini;

Patented Apr. 17, 1945 REAR-"ISION Toledo, Ohio,

2,374,027 DPTlCAL INSTRUMENT Harold a. McMaster and assignors to Frank A. Roiiman, Libbey-Owens-Ford Glass Company, Toledo, Ohio, a corporation of Ohio Application December 26, 1941, Serial No. 424,420

' 1 Claims. '(Cl. 88-72) The present invention relates to an optical instrument and more particularly to a device intended for rear vision purposes.

Primarily, the instrument has been designed field by mereiy glancing at the view-screen of said instrument placed before him, without the necessity of adjustment or focusing.

In aircraft and, for example, in a single occupant ship, the pilot quite often has practically unobstructed vision rear of his ship.

In accordance with the present invention, a rear vision from any of the positions he normal in the pilot's seat during maneuvering The main purpose of our invention is fragmentary vertical longitudinal,

Fig. .3 is a vertical transverse section therethrougls;

Fig. 4 is a fragmentary elevation of the instrument partly in section for purposes of illustration;

Fig. 5 is a. diagrammatic plan view of a part 0! the optical system;

Fig. 6 is similar to Fig. 5, illustrating the longitudinal field oi the particular system illustrated;

Fig. 7 is an enlarged sectional view of a cubical prism employed in the preferred system;

Fig. 8 is a front elevation of a modified instru ment; and

Fig. 9 is a vertical transverse the device shown in Fig. 8.

Referring first to Fig. 1, which will be understood to be purely diagrammatic and illustrative of only one application of the device, in this case a single seated fighter plane; the pilot A is seated in the pilots seat 50. The windshield is indicated by the numeral ii and between the windshield and pilot is shown a bullet-resistant laminated glass shield l2. The canopy of the ship is indicated generally by the numeral 53, and in this type of ship the canopy is fundamentally a glazed section through and indicated by the numeral M. The letter B is employed to designate the approximate position of the pilot's eyes when examining the gun sight II, and it is an important feature of our rear vision. periscope that the pilot may use it not only-*w'hen in his normal position in the seat but also when he moves forward to examine the gun sight or any of I pilot must assume during handling of his plane in ordinary flight and when in combat. The-broken lines D in Fig. 1 show how readily the pilot can see the view-screen when in one position, while screen itself is so made that the image thereon can be seen from these various positions.

Our rear vision periscope is indicated in its entirety by the letter C in Fig. 1. It will be noted that the perlscope is mounted in of a. single collecting lens.

of a, rear vision instrument is dependent not only upon the ease of image inspection but also and, as indicated in Fig. '1 by silvered and lacquered ait their interfaces. The

upon the range of field covered, lack of distortion, and brilliancy or clarity of image produced. Thus, the range of field covered with any given instrument is handled by a plurality of collecting devices so designed, mounted, and oriented as to superimpose the various images to produce a single, continuous, sharply defined image free of boundary lines, objectionable overlap, or distortion. That is, .there is no double image or breaks in the image produced.

By means of suitable reflecting devices properly associated, the superimposed images are reflected as a single image upon a view-screen. An important feature of the instrument is a view-screen having a translucent surface giving a clear, sharp image which is of substantially uniform intensityv over the entire screen and for all practical purposes such as not toresult in objectionable reflection of direct light.

area of the images, the prisms are then cemented perma-- Our periscope is further provided with breather means so that the instrument will not be injured or otherwise adversely affected when undergoing varying barometric pressures as are encountered when ships fly at different altitudes. The breather device includes dehydrating and filtering means so that moisture and othei foreign matter will not be permitted to enter within the instrument.

With further reference to Figs. 2 to 'I inclusive, the periscope shown has a casing i5 which may be of metal, plastic, or other materials capable of withstanding the necessary shocks. temperature changes, vibration, etc. For example, the construction of the instrument as a whole for use in an airplane need not ordinarily be as rugged aswhen used in a tank, but obviously the selection of materials and matters of this kind can be altered to meet particular needs.

In the particular instrument illustrated in these figures, five objective len systems are used. Without of course being restricted to exact sizes of lenses and with the further explanation that the optical system can be varied from that shown to cover a greater or lesser field either horizontally orvertically, or both, and that these factors are also influenced by the maximum over-all dimensions for the instrument permissible in any given installation, the system shown includes five 10- diopter pianoconvex lenses indicated by the numerals l8, l1, I8, i9 and 20. In a number of instruments made by us, these lenses measured approximately one-half inchby five-eighths inch and were about one-eighth inch thick at the center. All five of the lenses are mounted with their plano faces in a common plane and adjacent lenses are separated by non-reflecting, opaque strips 2|.

difficulty from stray light, it is of course preferred that all interior parts of the instrument except the lenses and mirrors be non-reflecting and, if necessary, the surfaces may be coated with flat black-paint.

Immediately in front of each of the lenses It to 20 is mounted ahalf inch cubical prism 22. These prisms are split along one diagonal the letter F, are

To prevent lacquer used by us to protect the silver films was black, but any other proper material can 'beused for this purpose.

As shown in Fig.3, the lenses Hi to 20 and prisms 22 are mounted between the casing Hi. When positioning the prism the plate 23 an a set screws (not shown) used to frictionally hold or clamp them in place between the plate 23 and the casing. When properly positioned, which mean the necessary orientation to give the desired superimposed position'of all of the nently ihto place.

The piano-convex lenses are also permanently cemented in place and, as shown, the casing It has a groove 24 adapted to receive one edge of the lens while the opposite edge is seated in the reduced end 25 of the plate 23. In addition to the cementing agent, the seats for the lenses may be provided with felt, cork, or other gasket and cushioning means. This is also true forthe cubical prisms in that satisfactory cushioning layers can be placed between the frame parts and the edges of the prisms, and all of the parts securely cemented against accidental displacement.

Fig. 3 shows the interior of the instrument clearly, and it will be observed that a mirror 26 i mounted within the casing to reflect the rays of light passing through the lens systems just described. In the particular design of instrument illustrated, where the periscope is to be mounted approximately as shown in Fig. 1, the mirror 26 is placed at an angle of 45 degree to the axis of the several lens systems. A

second mirror 21 is arranged as shown in Fig. 3, the two mirrors being cemented ,or clamped into position and-held against accidental displacement. The most effective type of mirror for the purpose is a front surface mirror of evaporated aluminum, such mirrors and the manufacture thereof being well known.

The view-screen of the instrument shown in Fig. 3 is designated by the numeral 28 and is in the form of a piano-cylindrical lens whose axis is horizontal. In one style of periscope which we have produced, ,a ten diopter plane-cylindrical lens was employed. The exterior surface 29 of this lens is given what may be termed a matte finish such as by sandblasting, grinding with abrasive material, or by acid etch treatment. It has been found that best results are obtained if the finish is a mild one suficient to kill the polish and to reduce to a minimum reflection of direct light, without being coarse or deeply pitted. The casing is preferably extended beyond the surface 29 of the lens in a manner to produce a light shield' or hood 30, intended primarily a) 1ptroteci', the view-screen from excessive direct As will be apparent, the more completely the view-screen is shielded from direct light, the

easier it will be to see the image, but our design of instrument does have the definite advantage that even when .the view-screen is not shielded at alLthe observer can see a well defined image on the view-screen if he is reasonably close to it and in a position where he can see the entire screen.

To protect the objective lenses, a cover plate 3| is used and as shown in liig. 3 is disposed at an angle for purposes of streamlining, and reference to Fig. 1 will show how well this is done. On the other hand, the cover plate is not a part of the optical system and can be mounted at right angles to the axis of the objective lenses which will give some gain in light transmission. When the instrument casing and parts are assembled, they should of course be cleaned and made to fit together tightly, and preferably all exterior joints are carefully cemented and scaled to prevent 7 /leakage of dust, moisture, etc. However, as a.

the instrument be vented to the i second surface resulting in reversal of the ver. lenses peri'scope or this kind usedin aircraft will be subjected to varying altitudes, it is important that outside. Toward'this end, we provide the instrument with a self-contained dehydrating cartridge 3iv which is in the form of a perforated tube adapted to contain a dehydrating agent 33 such as calciumchloride or other commonly used dehydrating agents. The tube may be soldered or otherwise held in place at one end as at 34, and the opposite end is mounted upon the threaded sleeve having a removable lug 36 provided witha relatively small vent ll therethrough. The plug can be removed to permit removal and replacement of the dehydrating material. The use of a restricted aperture is desirable because it prevents excessive movement of air'through the instrument but does allow for sufficient breathing to prevent dangerous pressures or lack of pressure within the instrument. As shown, the location of the breather tube is such as not to in any i. way interfere with the optical system.

All or part of the casing, mirrors, and other parts of the periscope may be protected with insulation 3B and an external covering 39, or any desired reinforcing structure.

Figs. 5 and 6 show diagrammatically the superimposing of the horizontal range of trates how caused to converge at a single point on the viewplurality of images and the field covered. Fig. ,5 illusscreen. Assuming that in Fig. 5, only the pianoconvex lenses were used, then light from a distant object would pass through each of the five lenses and form five separate images side by side on the view-screen, and said images would be reversed from right and left. However, when the the lenses and inclined prisms are placed before to the axes of the lenses as indicated in Fig, 5, the prisms cause the images to be superimposed and'appcar as a single image and also right and left hand relations are preserved.

'll "ig. 7 illustratesdiagrammatically how light entering one or the risms will be refracted at the first surface and reflected once from the silvercd diagonal, then again refracted at the image hut giving no dispersion or color.

advantage is taken of this single reflection to redirect the light rays so that the images will be superimposed. The hrilliancy of the final single image is enhanced by superimposing the plurality of images of the several lenses. v Advantage is also taken of this fact to keep the aperture of each lens small so that a simple lens may be used. 6 shows the horizontal field covered by an arrangement of live prisms and five plano-con-= The angle so covered could be increased by increaslngthe number of lenses and prisms, and in fact can he carried to the point when a panorama of 18d degrees could be viewed on a single fiat view plate. The vertical field, however, would be no greater than that which a single lens would cover. Due to the small aperture of the individual lenses, the vertical angle may he degrees tor a simple lens or greater still for acorrected lens.

The image formed by an arrangement as shown in Figs. 5 and 6 would be inverted, but in the actual instrument two mirrors are placed in the light path to reinvert the image of make it erect. The flnal image, as seen on the view-screen, is then oriented in a similar manner to that in the conventional automobile rear-view mirror. The view-screen is made in the form of a cylindrical parallel light from a distant point is In practice, We finish to get satisfactory brilliance 1 single lens is lens so that the row of small objective lenses will appear to cover the whole screen and illuminate it uniformly. Were it not for the matte finish on the piano surface of this cylindrical lens, it would be necessary for the observer to place s eyes directly on the axis of the system before he could see the image formed by the system, and any slight displacement therefrom would result in his losing the view. When the piano surface of the cylindrical lens has a matte finish, however, and the image is sharply focused thereon, the light is difiused throughout a considerable angle and the image is visible throughout a hemisphere of 186 degrees in all directions, although the brilliancy diminishes as the observer departs substantially from'the axis of the system. If the matte finish is coarse, hri-lliancy of the image suffers but is more readily discernible over a wider range while, on the other hand, if the finish is line the image wilLhave a higher degree of brilliance when viewed onthe axis but will not be as readily discernible over as wide a field. have used an intermediate matte in a relatively wide angle of viewing positions.

In the simple form indicated in Fig. 9, no

prisms are used and the image formed by the erect but has right and left hand reversed. The angular size of the field covered by such a periscope is limited to that covered by a single lens. The lens Mi is mounted in the casing ll within which the mirrors 42 and A3 are positioned to reflect the image upon the viewscreen St. The screen illustrated is also of a simplified nature, being a fiat sheet of glass whose outer surface is provided with a matte finish similar to the surface as of the lens 28. Obviously, the flat view-screen can be used in lieu of the lens in either construction, or vice-versa.

We contemplate the treatment or the lenses used in the systems to reduce glare or, stated difierently; to increase light transmission. For example, the surfaces of the lenses maybe given a light etch or base coatings applied thereon capable of increasing the light transmission or the parts without interferingwith the optical properties thereof.

It is to be understood that the form of the invention herewith shown and described is to be taken as the preferred embodiment oi. the some,

and that various changes in the shape, size and 1. An optical instrument of the class described comprising a view-screen, a plurality of objective collecting lenses each of which includes a prism having a light reflecting diagonal, and reflecting means for directing light rays passing through said objective lenses upon the view-screen, the objective lenses being so positioned that a single image is formed upon the view-screen.

2. An. optical instrument of the class described comprising 'a view-screen having a matte finish 3 surface through which light may pass, a plurality of objective lenses each of which includes a cubical prism having a light reflecting diagonal, and a plurality of reflecting means for directing light rays passing through said objective lenses upon the matte finish surface of the view-screen to produce a properly oriented image thereon. saidobjective lenses being so positioned that a single image is formed upon the view-screen.

3. An optical instrument of the class described jective lenses upon the view-screen where a single properly oriented image is produced.

4. An optical instrument of the class described comprising a plane-cylindrical lens having a horizontal axis, the plano surface being arranged the exterior ofthe instrument and having a matte finish surface through which light may pass, a plurality of objective lenses each of which comprises a. lano-convex lens and a cubical prism having a light reflecting diagonal, the axis of the piano-cylindrical lens being difierent from that of the objective lenses, and a pair of light reflecting platesffor directing the light rays passing through said objective lenses upon the matte finish surface of the piano-cylindrical lens to produce a single, properly oriented image thereon.

5. An optical instrument of the class described comprising a view-screen havinga. matte finish surface through which light rays may pass, a plurality of spaced objective lenses each or which comprises a plano-convex lens and a cubical prism having a light reflecting diagonal, the piano surfaces of the piano-convex lenses of said objectives being disposed in a common plane, the cubical prisms being inclined to the axes of said plano-convex lenses to cause the plurality of images produced by said objectives to be superimposed and appear as a single image upon the view-screen. i i

6. An optical instrument of the class described i V rality of spaced objective piano-convex lenses to cause the plurality of images produced by said objectives to be superimposed and appear as a single image upon the view-screen, and an opaque separator disposed between adjacent objective lenses.

7. An optical instrument of the class described comprising a view-screen having a matte finish surface through which light rays may pass, a plurality of spaced objective lenses each of which comprises a plane-convex lens and a cubical prism having a light reflecting diagonal, the plano surfaces of the piano-convex lenses of said objectives being disposed in a common plane, the cubical prisms being inclined to the axes of said piano-convex lenses to cause. the plurality of images produced by said objectives to ,besuperimposed and appear as a single image upon the view-screen, an opaque separator disposed between adjacent objective lenses, and means between the objective lenses and view-screen for reinverting the images formed by the robjective lenses so that the continuous image on the viewscreen will be correct as to top and bottom and from right to left.

HAROLD A. MOMASTER. FRANK A. RODMAN.

finish the cubical prisms being inclined to the axes of said 

